This disclosure relates to components for radio frequency signals in the microwave region. Specifically, a radio frequency (R.F.) circulator is disclosed comprising a ferromagnetic magnetic metal-insulator laminate structure which does not require an external magnetic field.
R.F. circulators are used in the processing of microwave signals as passive isolators that convey an electromagnetic wave in a single direction. This property allows a transmitter and receiver to share the same antenna. For instances, power from the transmitter applied to one port will go to a second antenna port of a three port circulator, and received energy the second port from the antenna will be directed to a third port of the circulator.
Conventional circulators use ferrites having an external biasing magnetic field. The circulator is essentially a circular capacitor where the material between the metal electrodes is made of ferrite, having a magnetization aligned perpendicular to the plane by an external biasing magnetic field. The device operates as a resonant cavity, where the resonant frequency for an electromagnetic wave going in the clockwise direction is different from that going in the counter clockwise direction. The operating frequency of the R.F. signal is close to one of the resonant frequencies to give the device its directional propagating properties.
The behavior of magnetic material for left/right-handed circularly polarized radiation produces the unidirectional circulator properties. As the frequency of the R.F. signal increases to a frequency comparable to the spin wave frequency of the ferrite, losses in efficiency occur. While magnetic metals have high spin wave frequencies, it is not possible to replace the insulating ferrite by a metal as the eddy current losses in a metal at lower frequencies will effectively limit the useful frequency range for the circulator.
Embodiments of this disclosure have been developed to reduce the losses incurred from eddy current generation in ferromagnetic metals and losses due to the lower spin wave frequency of the ferrites.